19-1676; Rev 4; 6/10
Pin-Selectable Watchdog Timers
General Description
The MAX6369–MAX6374 are pin-selectable watchdog
timers that supervise microprocessor (µP) activity and
signal when a system is operating improperly. During
normal operation, the microprocessor should repeated-
ly toggle the watchdog input (WDI) before the selected
watchdog timeout period elapses to demonstrate that
the system is processing code properly. If the µP does
not provide a valid watchdog input transition before the
timeout period expires, the supervisor asserts a watch-
dog (WDO) output to signal that the system is not exe-
cuting the desired instructions within the expected time
frame. The watchdog output pulse can be used to reset
the µP or interrupt the system to warn of processing
errors.
The MAX6369–MAX6374 are flexible watchdog timer
supervisors that can increase system reliability through
notification of code execution errors. The family offers
several pin-selectable watchdog timing options to
match a wide range of system timing applications:
• Watchdog startup delay: provides an initial delay
before the watchdog timer is started.
• Watchdog timeout period: normal operating watch-
dog timeout period after the initial startup delay.
• Watchdog output/timing options: open drain (100ms)
or push-pull (1ms).
The MAX6369–MAX6374 operate over a +2.5V to +5.5V
supply range and are available in miniature 8-pin
SOT23 packages.
Features
♦
Precision Watchdog Timer for Critical
µP
Applications
♦
Pin-Selectable Watchdog Timeout Periods
♦
Pin-Selectable Watchdog Startup Delay Periods
♦
Ability to Change Watchdog Timing Characteristics
Without Power Cycling
♦
Open-Drain or Push-Pull Pulsed Active-Low
Watchdog Output
♦
Watchdog Timer Disable Feature
♦
+2.5V to +5.5V Operating Voltage
♦
8µA Low Supply Current
♦
No External Components Required
♦
Miniature 8-Pin SOT23 Package
MAX6369–MAX6374
Ordering Information
PART
MAX6369KA-T
MAX6369KA/V-T
MAX6369KA/V+T
MAX6370KA-T
MAX6371KA-T
MAX6372KA-T
MAX6373KA-T
MAX6374KA-T
TEMP
RANGE
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
-40°C to +125°C
PIN-
PACKAGE
8 SOT23
8 SOT23
8 SOT23
8 SOT23
8 SOT23
8 SOT23
8 SOT23
8 SOT23
TOP
MARK
AADC
AADC
AADC
AADD
AADE
AADF
AADG
AADH
________________________Applications
Embedded Control Systems
Industrial Controllers
Critical µP and Microcontroller (µC) Monitoring
Automotive
Telecommunications
Networking
Note:
All devices are available in tape-and-reel only. Required
order increment is 2,500 pieces.
/V denotes an automotive qualified part.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
Pin Configuration appears at end of data sheet.
Selector Guide
PART
MAX6369
MAX6370
MAX6371
MAX6372
MAX6373
MAX6374
OUTPUT
Open Drain
Push-Pull
Open Drain
Push-Pull
Open Drain
Push-Pull
WDO PULSE
WIDTH (ms)
100
1
100
1
100
1
MINIMUM STARTUP DELAY
Selectable: 1ms to 60s
Selectable: 1ms to 60s
60s
60s
Selectable: 200µs to 60s or first edge
Selectable: 200µs to 60s or first edge
MINIMUM WATCHDOG TIMEOUT
Selectable: 1ms to 60s
Selectable: 1ms to 60s
Selectable: 1ms to 60s
Selectable: 1ms to 60s
Selectable: 30µs to 10s
Selectable: 30µs to 10s
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Pin-Selectable Watchdog Timers
MAX6369–MAX6374
ABSOLUTE MAXIMUM RATINGS
Terminal Voltage (with respect to GND)
V
CC
.....................................................................-0.3V to +6V
WDI.....................................................................-0.3V to +6V
WDO
(Open Drain: MAX6369/71/73) .................-0.3V to +6V
WDO
(Push-Pull: MAX6370/72/74 .......-0.3V to (V
CC
+ 0.3V)
SET0, SET1, SET2 ................................-0.3V to (V
CC
+ 0.3V)
Maximum Current, Any Pin (input/output)...........................20mA
Continuous Power Dissipation (T
A
= +70°C)
8-Pin SOT23 (derate 8.75mW/°C above +70°C).........700mW
Operating Temperature Range .........................-40°C to +125°C
Storage Temperature Range .............................-65°C to +150°C
Junction Temperature ......................................................+150°C
V
CC
Rise or Fall Rate......................................................0.05V/µs
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow)
Lead(Pb)-free...................................................................+260°C
Containing Lead (Pb).......................................................+240°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(V
CC
= +2.5V to +5.5V, SET_ = V
CC
or GND, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C and
V
CC
= +3V.) (Note 1)
PARAMETER
Operating Voltage Range
Supply Current
Input High Voltage
SYMBOL
V
CC
I
CC
V
IH
No load
T
A
= -40°C to +85°C
T
A
= -40°C to +125°C
WDI, SET0, SET1, SET2
V
CC
≥
3.3V,
T
A
= -40°C to +85°C
WDI, SET0,
SET1, SET2
V
CC
≥
3.3V,
T
A
= -40°C to +125°C
V
CC
≥
2.5V,
T
A
= -40°C to +85°C
V
CC
≥
2.5V,
T
A
= -40°C to +125°C
Logic Input Current (Note 2)
WDO
Output Low
Voltage
V
WDI
or V
SET_
= 0V or V
CC
I
SINK
= 1.2mA, V
CC
> 2.7V, watchdog
output asserted
V
OL
I
SINK
= 6mA, V
CC
> 4.5V, watchdog
output asserted
V
WDO
= 0 to +5.5V, output deasserted,
MAX6369/MAX6371/MAX6373
I
SOURCE
= 500µA, V
CC
> 2.7V, watchdog
output deasserted
V
OH
I
SOURCE
= 800µA, V
CC
> 4.5V, watchdog
output deasserted
0.8
×
V
CC
V
V
CC
- 1.5
0
0.8
×
V
CC
0.8
0.6
V
0.6
0.4
±10
0.3
0.4
1
nA
V
V
µA
CONDITIONS
MIN
2.5
8
10
TYP
MAX
5.5
20
µA
22
V
UNITS
V
Input Low Voltage
V
IL
WDO
Leakage Current
I
LKG
WDO
Output High
Voltage
2
_______________________________________________________________________________________
Pin-Selectable Watchdog Timers
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.5V to +5.5V, SET_ = V
CC
or GND, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C and
V
CC
= +3V.) (Note 1)
PARAMETER
MAX6369/MAX6370
V
SET2
= 0V, V
SET1
= 0V, V
SET0
= 0V
V
SET2
= 0V, V
SET1
= 0,V SET0 = V
CC
V
SET2
= 0V, SET1 = V
CC
, V
SET0
= 0V
Startup Delay Period
t
DELAY
V
SET2
= 0V, SET1 = V
CC
, SET0 = V
CC
SET2 = V
CC
, V
SET1
= 0V, V
SET0
= 0V
SET2 = V
CC
, V
SET1
= 0V, SET0 = V
CC
SET2 = V
CC
, SET1 = V
CC
, V
SET0
= 0V
SET2 = V
CC
, SET1 = V
CC
, SET0 = V
CC
V
SET2
= 0V, V
SET1
= 0V, V
SET0
= 0V
V
SET2
= 0V, V
SET1
= 0V, SET0 = V
CC
V
SET2
= 0V, SET1 = V
CC
, V
SET0
= 0V
Watchdog Timeout
Period
t
WD
V
SET2
= 0V, SET1 = V
CC
, SET0 = V
CC
SET2 = V
CC
, V
SET1
= 0V, V
SET0
= 0V
SET2 = V
CC
, V
SET1
= 0V, SET0 = V
CC
SET2 = V
CC
, SET1 = V
CC
, V
SET0
= 0V
SET2 = V
CC
, SET1 = V
CC
, SET0 = V
CC
MAX6371/MAX6372
Startup Delay Period
t
DELAY
V
SET2
= 0V, SET1 = V
CC
, SET0 = V
CC
All other SET_ conditions
V
SET2
= 0V, V
SET1
= 0V, V
SET0
= 0V
V
SET2
= 0V, V
SET1
= 0V, SET0 = V
CC
V
SET2
= 0V, SET1 = V
CC
, V
SET0
= 0V
Watchdog Time-Out
Period
t
WD
V
SET2
= 0V, SET1 = V
CC
, SET0 = V
CC
SET2 = V
CC
, V
SET1
= 0V, V
SET0
= 0V
SET2 = V
CC
, V
SET1
= 0V, SET0 = V
CC
SET2 = V
CC
, SET1 = V
CC
, V
SET0
= 0V
SET2 = V
CC
, SET1 = V
CC
, SET0 = V
CC
MAX6373/MAX6374
V
SET2
= 0V, V
SET1
= 0V, V
SET0
= 0V
V
SET2
= 0V, V
SET1
= 0V, SET0 = V
CC
V
SET2
= 0V, SET1 = V
CC
, V
SET0
= 0V
Startup Delay Period
t
DELAY
SET2 = 0V, SET1 = V
CC
, SET0 = V
CC
SET2 = V
CC
, V
SET1
= 0V, V
SET0
= 0V
SET2 = V
CC
, V
SET1
= 0V, SET0 = V
CC
SET2 = V
CC
, SET1 = V
CC
, V
SET0
= 0V
SET2 = V
CC
, SET1 = V
CC
, SET0 = V
CC
3
3
60
200
Watchdog Disabled
600
µs
First Edge (Note 3)
First Edge (Note 3)
60
180
s
9
9
180
ms
s
Watchdog Disabled
60
1
3
10
100
300
3
60
Watchdog Disabled
300
900
9
180
ms
s
180
3
9
30
ms
s
1
10
30
100
1
10
60
1
10
30
100
1
10
60
3
30
90
300
3
30
180
3
30
90
300
3
30
180
s
ms
ms
s
ms
ms
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX6369–MAX6374
Watchdog Disabled
Watchdog Disabled
_______________________________________________________________________________________
3
Pin-Selectable Watchdog Timers
MAX6369–MAX6374
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.5V to +5.5V, SET_ = V
CC
or GND, T
A
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C and
V
CC
= +3V.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
V
SET2
= 0V, V
SET1
= 0V, V
SET0
= 0V
V
SET2
= 0V, V
SET1
= 0V, SET0 = V
CC
V
SET2
= 0V, SET1 = V
CC
, V
SET0
= 0V
Watchdog Timeout
Period
t
WD
V
SET2
= 0V, SET1 = V
CC
, SET0 = V
CC
SET2 = V
CC
, V
SET1
= 0V, V
SET0
= 0V
SET2 = V
CC
, V
SET1
= 0V, SET0 = V
CC
SET2 = V
CC
, SET1 = V
CC
, V
SET0
= 0V
SET2 = V
CC
, SET1 = V
CC
, SET0 = V
CC
Watchdog Input Pulse Width
(Note 2)
Watchdog Output Pulse Width
Internal Setup Time
(Note 4)
t
WDI
t
WDO
t
SETUP
After
WDO
deasserted
MAX6369/MAX6371/MAX6373
MAX6370/MAX6372/MAX6374
After
WDO
deasserted
MIN
3
3
1
Watchdog Disabled
30
1
10
10
100
100
1
100
300
3
300
90
3
30
30
ns
ms
ms
ms
s
µs
TYP
MAX
9
9
3
UNITS
ms
s
Note 1:
Production tested at T
A
= +25°C. Guaranteed by design over temperature limits.
Note 2:
Guaranteed by design.
Note 3:
In this setting the watchdog timer is inactive and startup delay ends when WDI sees its first level transition. See the
Selecting
Device Timing
section for more information.
Note 4:
After power-up, or a setting change, there is an internal setup time during which WDI is ignored.
Typical Operating Characteristics
(Circuit of Figure 1, T
A
= +25°C, unless otherwise noted
.)
SUPPLY CURRENT
vs. TEMPERATURE
MAX6369/74-01
WATCHDOG TIMEOUT PERIOD
vs. TEMPERATURE
NORMALIZED WATCHDOG TIMEOUT PERIOD
MAX6369/74-02
14
1.003
1.002
1.001
1.000
0.999
0.998
0.997
12
SUPPLY CURRENT (µA)
V
CC
= +5.5V
10
8
V
CC
= +2.5V
6
4
-40
-15
10
35
60
85
TEMPERATURE (°C)
-40
-15
10
35
60
85
TEMPERATURE (°C)
4
_______________________________________________________________________________________
Pin-Selectable Watchdog Timers
Pin Description
PIN
1
2
3
4
5
6
7
8
NAME
WDI
GND
N.C.
SET0
SET1
SET2
WDO
V
CC
FUNCTION
Watchdog Input. If WDI remains either high or low for the duration of the watchdog timeout period (t
WD
),
WDO
triggers a pulse. The internal watchdog timer clears whenever a
WDO
is asserted or whenever WDI sees a
rising or falling edge.
Ground
Not Connected. Do not make any connection to this pin.
Set Zero. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.
Set One. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.
Set Two. Logic input for selecting startup delay and watchdog timeout periods. See Table 1 for timing details.
Watchdog Output. Pulses low for the watchdog output pulse width, t
WDO
, when the internal watchdog times
out. The MAX6369/MAX6371/MAX6373 have open-drain outputs and require a pull-up resistor. The
MAX6370/MAX6372/MAX6374 outputs are push-pull.
Supply Voltage (+2.5V to +5.5V)
MAX6369–MAX6374
Table 1. Minimum Timeout Settings
LOGIC INPUTS
SET2
0
0
0
0
1
1
1
1
SET1
0
0
1
1
0
0
1
1
SET0
0
1
0
1
0
1
0
1
MAX6369/MAX6370
t
DELAY
, t
WD
1ms
10ms
30ms
Disabled
100ms
1s
10s
60s
MAX6371/MAX6372
t
DELAY
= 60s, t
WD
1ms
3ms
10ms
Disabled
100ms
300ms
3s
60s
MAX6373/MAX6374
t
DELAY
3ms
3s
60s
Disabled
200µs
First Edge
First Edge
60s
t
WD
3ms
3s
1s
Disabled
30µs
1s
10s
10s
Detailed Description
The MAX6369–MAX6374 are flexible watchdog circuits
for monitoring µP activity. During normal operation, the
internal timer is cleared each time the µP toggles the
WDI with a valid logic transition (low to high or high to
low) within the selected timeout period (t
WD
). The
WDO
remains high as long as the input is strobed within the
selected timeout period. If the input is not strobed
before the timeout period expires, the watchdog output
is asserted low for the watchdog output pulse width
(t
WDO
). The device type and the state of the three logic
control pins (SET0, SET1, and SET2) determine watch-
dog timing characteristics. The three basic timing varia-
tions for the watchdog startup delay and the normal
watchdog timeout period are summarized below (see
Table 1 for the timeout characteristics for all devices in
the family):
• Watchdog Startup Delay:
Provides an initial delay before the watchdog timer is
started.
Allows time for the µP system to power up and initial-
ize before assuming responsibility for normal watch-
dog timer updates.
Includes several fixed or pin-selectable startup delay
options from 200µs to 60s, and an option to wait for
the first watchdog input transition before starting the
watchdog timer.
5
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